1. Field of the Invention
The present invention relates to a transistor array, the manufacturing method thereof and an image processor which uses the same. More particularly, the present invention relates to the element structure of a transistor array configuration comprising polysilicon thin-film transistors and amorphous silicon thin-film transistors, the associated manufacturing method and an image processor that applies the aforesaid transistor array.
2. Description of the Related Art
Recently, Research and Development (R&D) has become more highly advanced for applying personal authentication technology (biometric technology) to identify a specific individual using a “living characteristic” of a person's body data including fingerprint scans. Due to the public's ever-increasing security and privacy concerns, personal authentication has become essential in providing secure services such as electronic banking, credit card transactions, etc.
Meanwhile in past few years, Liquid Crystal Displays (LCDs) and plasma displays have experienced phenomenal growth in use as displays and video device monitors for such items as personal computers, televisions, etc. Furthermore, R&D is rapidly moving toward proliferation and full-scale utilization of a display which applies self-luminescence devices as the next generation of display devices such as organic electroluminescent devices (hereinafter, denoted as “organic EL devices”), Light Emitting Diodes (LEDs), etc.
As applied to the personal authentication technology (fingerprint authentication technology) mentioned above, an image processor, an LCD, or an image display device composed of an organic EL display for example is formed on the substrate insulation of a glass substrate. Also, the pixel array is composed of display pixels or photosensor reading pixels in a two-dimensional array and has a configuration comprising a driver circuit for driving the pixel array.
Here, for instance, to promote lower cost or miniaturization of image display devices, development of an image display device with a hybrid driver circuit is actively being designed and put in practical use which integrates the driver circuit on the same substrate as the integral display pixels. In an LCD with such a hybrid driver circuit, a configuration is known in which the driver circuit composes polysilicon thin-film transistors; whereas the driver elements in the display pixels compose amorphous silicon thin-film transistors. In this case, while acquiring relatively favorable operating characteristics by using polysilicon thin-film transistors for the driver circuit, stabilized driver element operating characteristics can be obtained by using amorphous silicon thin-film transistors for the driver elements in the display pixels.
However, in the image processor and/or the image display device stated above, both apparatus have disadvantages as defined in the following justification. Namely, in the preceding configuration wherein the driver circuit is composed using polysilicon thin-film transistors and the driver elements in the display pixels of the pixel array are composed using amorphous silicon thin-film transistors with the polysilicon thin-film transistors and the amorphous silicon thin-film transistors formed together on a common substrate. In this case, the polysilicon thin-film transistors are fabricated in a polysilicon layer by crystallizing, for example by laser irradiation, the amorphous silicon film formed on the substrate. Because these ▪@devices (components) are formed using this polysilicon layer, insofar as fabricating the amorphous silicon thin-film transistors and the polysilicon thin-film transistors on a single substrate, the polysilicon thin-film transistors are formed by selectively crystallizing only the driver circuit formation areas after the amorphous silicon film is formed on the substrate. Thus a ▪@separate processing step is needed to partially create the polysilicon layer. For this reason, during crystallization of the amorphous silicon film by laser irradiation for instance, it is necessary to selectively crystallize the amorphous silicon film using a thin laser beam scan while controlling the laser radiator position with high precision. Accordingly, there is a disadvantage in needing highly accurate manufacturing equipment which requires a relative lengthy period to accomplish the crystallizing process and ultimately adds to the production costs.
Furthermore, when annealing the amorphous silicon film, it is difficult to separate distinctly between the areas to crystallize and the areas not to crystallize as this process is performed by preheating the amorphous silicon film to a temperature in the order of 600 degrees Celsius. Accordingly, there is a disadvantage in that it is difficult to arrange the driver circuit composed of polysilicon thin-film transistors and the pixel array composed of amorphous silicon thin-film transistors within sufficient proximity on the substrate.